According to current construction practice, concrete structures such as foundation grade beams, columns, suspended and spandrel beams and concrete float structures, are cast in place in a conventional timber or steel pan formwork system. Precasting off-site is another common concrete structure manufacturing technique.
A conventional foundation grade beam may be used to support, for example, the exterior wall and upper structure of a building. A grade beam is a cast in place structure reinforced with mild steel rods. A standard type grade beam may have a standard cross-section of 8 in. width and 24 in. depth. The span length between intermediate supports such as footings or piles is variable but is usually anywhere from 12 to 36 ft.
The grade beam is typically cast in place in a pre-formed elaborate timber or steel pan formwork system which is time consuming and labour intensive to construct. A conventional timber formwork system can only be used six or seven times before it deteriorates to the point where it must be discarded. New timber formwork is then erected and used. Steel pan formwork does not deteriorate with repeated use, but is expensive and labour intensive to install. The concrete grade beam is reinforced throughout its length in both the upper and lower regions with horizontally placed steel rods and vertical stirrups.
The grade beam sections are cast in a conventional formwork system of timber or steel pan construction which are assembled and erected in place, aligned, plumbed, and adequately braced prior to placement of reinforcing steel and concrete within the interior of the formwork. After the concrete grade beam has been poured in place, the formwork is then dismantled after the concrete has reached an adequate set. The formwork is then positioned and reassembled to continue the previously poured in place concrete beam section, and prepared for the next pour.
The conventional way to construct a standard timber or steel pan formwork system, and pour a standard steel reinforced rectangular cross-section grade beam has a number of disadvantages:
1. The assembly and dismantling of the formwork is labour and time intensive. PA0 2. The reuse potential of the formwork materials is limited. PA0 3. The formwork does not efficiently adapt to heat or steam cure methods. PA0 4. The rectangular cross-section of a conventional grade beam has always been the easiest shape to form by conventional methods, but it is structurally inefficient and uses more concrete than is necessary to achieve design strength. (At least 25% more concrete than necessary is required in a standard 8" by 24" cross-section grade beam).